Since they were first implemented, that is, since about the end of the 19th century, products of the aforementioned type have undergone various modifications and development, particularly regarding the bituminous binding mass impregnating or coating the core.
Thus, this binding mass consisted initially of oxidized bitumen. Then from the 1960-1970s onwards, the binding mass consisted of a mixture [bitumen+atactic polypropylene (APP)] and since about 1975 binding masses based on mixtures [bitumen+SBS polymer (styrene-butadiene-styrene)] have become widespread.
However, atactic polypropylenes are not particularly compatible with bitumen, are not always easily available in large quantities and have a particular behavior when hot (with a high melting point) associated with a sharp reduction in viscosity. The strength of the seams of this type of membrane remains to this day a technical problem that is not completely solved.
As for SBS elastomeric polymers, these have numerous advantageous properties, namely high elasticity, great durability, good workability and high availability in terms of resources.
Nevertheless, these substances have a major drawback in the context of applications of the aforementioned products: they are sensitive to UV (ultraviolet). In fact, butadiene has unsaturated double carbon/carbon bonds which are susceptible to UV.
Under the combined effect of UV, temperature variations and humidity; waterproofing membranes based on a bitumen/SBS binder subjected to atmospheric or climatic agents therefore rapidly show microcrazing, in the absence of a special surface protection layer, which damages the aesthetic appearance and continued waterproofing qualities of said membranes.
To overcome this drawback, waterproofing membranes based on a bitumen/SBS binder are at present, in a known manner, covered with a layer of flakes (mineral, organic or metallic) or with a metallic laminate, which are incorporated during manufacture in the surface of said membranes. Membranes based on SBS-modified bitumen that do not have such auto-protection must at present be protected from UV on site by a removable protection (surfacing, revegetation, fine gravel, etc.).
This added protection, known as auto-protection, generates significant extra weight (generally of approximately 1 kg/m2), produces a free fraction which may block the rainwater disposal means and prevent the production of sealed jointing by partial overlap of adjacent membranes (the flakes must be removed along the longitudinal edges and in the region of the end transversal zones of said membranes).
The problem posed for the present invention therefore consists of providing a bituminous waterproofing membrane based on a bitumen/elastomer binder, that has in particular good UV resistance without specific auto-protection, good workability and good performance over time, from the point of view of both waterproofing and visual appearance, while advantageously allowing laying with partial lateral overlap and positive connection by heating.
The invention will be better understood with the help of the description below, which relates to preferred embodiments, given as non-limiting examples, and explained with reference to the accompanying drawings, in which: